The use of a grinding device for grinding polymeric material is well known. According to a prior polymer grinding device, polymer to be ground is fed axially to a rotating plate on which are mounted a ring of grinding blades. The axially fed polymer is forced outwardly along the rotating plate to the grinding blades. Arranged tangentially with respect to the rotating plate is a perforated shear plate. Polymer which has been forced outwardly to the grinding blades is caught between the outer edges of the grinding blades and the perforations in the shear plate and is accordingly sheared to smaller particle sizes. Due to extremely close tolerance requirements between the outer edges of the grinding blades and the perforated shear plate and the absence of means for effectively adjusting the grinding blades radially outwardly, these blades have been discarded when they become worn.